Effects of harvest time and nutrient supply on fuel quality of Paludiculture plant species

Paludiculture („palus" lat. swamp) is the sustainable use of wet and rewetted peatlands which maintains the peatbody for carbon storage. Worldwide, drained peatlands cover only 0.3 percent of the land area but emit almost 5 percent of all anthropogenic greenhouse gas emissions. Rewetting of drained peatlands is therefore an urgent need  for climate change mitigation. The production of biomass for the use as solid biofuel for combustion, is one promising utilisation option.

Compared to wood, herbaceous biomass (e.g. grasses and reeds) contains higher concentrations of critical elements (N, S, Cl or K) that leads to higher emissions (SO_x, NO_x) or to the destruction of boilers or parts of it (corrosion). Late harvest in winter is often recommended for grass species to improve fuel quality and also storage stability. Nutrients and other elements will be reduced in plant tissues by leaching or translocation processes during plant die-off. Water content that is crucial for storage will also decrease. Combustion quality of herbaceous biomass depends on plant species, site specific parameters and harvest time. There are only a few studies for the suitability of Paludiculture plants for combustion, and little is known about the effects of nutrient supply.

In our study we focused on fuel quality parameters of Typha latifolia, Typha angustifolia, Arundo donax, and four European clones of Phragmites australis (Denmark, Netherlands, Romania, and Italy) grown in mesocosms on three different nutrient levels (0, 75 and 500 kg N/ha/a). We analysed the total concentrations of C, H, N, O, S, Cl, K, Na, P, Ca, Si and ash content as well as higher heating value in the above ground biomass.

Winter harvested P. australis (Italy), T. angustifolia as well as T. latifolia could meet the required treasure values for N concentrations at all nutrient levels. S concentrations were only for T. angustifolia and T. latifolia below the treasure values at summer harvest, but for all plant species at winter harvest. Ash contents were very high for all plant species in summer (>6 %) – except for A. donax and P. australis (Netherlands). Effects of nutrient levels on biofuel quality were stronger in summer than in winter.

A comparison of plant species, harvest time (summer and winter) and nutrient levels will be used to decide for an optimal cultivation type and management strategy for Paludiculture purposes. The main aim is to provide biomass for combustion with high energy yields per hectare combined with the highest possible fuel quality.